The directive:
#ifndef __cplusplus
#error C++ is required
#elif __cplusplus < 201402L
#error C++14 is required
#endif
The command-line: g++ -Wall -Wextra -std=c++14 -c -o header.o header.hpp
My g++ version: g++ (tdm-1) 4.9.2
The error C++14 is required
is generated even when I added -std=c++14
, I don't know why.
Please tell me how to fix this.
According to the GCC CPP manual (version 4.9.2 and 5.1.0):
__cplusplus
This macro is defined when the C++ compiler is in use. You can use__cplusplus
to test whether a header is compiled by a C compiler or a C++ compiler. This macro is similar to__STDC_VERSION__
, in that it expands to a version number. Depending on the language standard selected, the value of the macro is199711L
, as mandated by the 1998 C++ standard;201103L
, per the 2011 C++ standard; an unspecified value strictly larger than201103L
for the experimental languages enabled by-std=c++1y
and-std=gnu++1y
.
You can check that g++ --std=c++14
defines __cplusplus
as:
Version __cplusplus
4.8.3 201300L
4.9.2 201300L
5.1.0 201402L
For clang++ --std=c++14
:
Version __cplusplus
3.3 201305L
3.4 201305L
3.5.x 201402L
3.6 201402L
3.7 201402L
So a safer check should probably be:
#ifndef __cplusplus
# error C++ is required
#elif __cplusplus <= 201103L
# error C++14 is required
#endif
As specified in the comment, this could mean partial C++14 support.
To check for a specific feature you could also try Boost Config (especially Macros that describe C++14 features not supported).